I. Field of the Invention
The invention relates to a displacement unit for at least one element to be displaced (hereinafter xe2x80x9cdisplaced elementxe2x80x9d), such as a carrier for optical elements, etc.
II. Background of the Invention
Displacement units of this kind are often used in precision engineering. In microscopy, for example, motorized displacement units are needed to move or pivot optical deflection prisms, optical subassemblies for focusing and/or focal length adjustment of objectives, dark slides, filters or other components of a microscope, or to switch them between different (and in particular between two) positions. For that purpose, known displacement units include a drive unit which drives a transfer element having a thread or a tooth set. An engagement element engages into the thread or tooth set in such a way that it is caused to move by motion of the transfer element. The motion of the transfer element then results in a motion of the displaced element.
In the case of many known displacement units, especially those in precision engineering or optics, the displacement or switchover must occur relatively quickly, and the positions to be arrived at must often be attained with high accuracy. In precision engineering and in optics, high-precision and therefore expensive components are used for this purpose. Above all, however, in the event of a malfunction such as, for example, contact by one or more parts of the unit against a stop, the displacement unit must not be damaged or xe2x80x9cjam.xe2x80x9d Jamming is a substantial problem, since in this case the displacement unit cannot be put back into operation without complete disassembly.
Known displacement units therefore comprise electronic safety circuits which have sensors, limit value transducers, etc. which shut off the motor of the drive unit when the displaced element makes contact against a stop or an obstacle. Jamming of the displacement unit can nevertheless occur in the event of a malfunction of the sensors or the limit value transducers, or other electronic malfunctions, because parts of the displacement unit are in physical contact against the mechanical stop or the obstacle, such that the displacement unit necessarily jams as a result of the force of the motor that does not switch off due to the malfunction.
Thus, it is an object of the invention to develop a displacement unit such that in the event of contact against a stop or an obstacle, the displacement unit neither jams nor is otherwise damaged.
A manner of achieving this object according to the present invention is provided comprising a drive unit, a transfer element that is caused to move by the drive unit and that comprises a thread or a tooth set, and an engagement element, which engages into the thread or tooth set of the transfer element and is thus driven by the motion of the transfer element, and by means of whose motion the displaced element is moved. The engagement element is configured elastically, in such a way that it deforms elastically upon contact by the displaced element against a stop or obstacle;
A particularly preferred use of the invention is in a microscope, and in particular in an automated microscope.
An underlying idea of the invention is to prevent xe2x80x9cjammingxe2x80x9d of or other damage to a displacement unit, upon contact by the carrier (for example of optical elements) or by another part of the displacement unit against a stop or an obstacle, by means of an elastic configuration of the engagement element (i.e., to perform the safety function mechanically). To implement this idea according to one aspect of the present invention, the engagement element is configured elastically, in such a way that it deforms elastically upon contact by the displaced element against a stop or an obstacle. This configuration makes it possible to arrive against a stop with a deliberate xe2x80x9coverrunxe2x80x9d of the motor, so that the displacement unit is pushed gently against the stop and is thus accurately positioned.
As a result of this configuration, jamming of or damage to parts of the displacement unit can be reliably prevented or reduced, even without an electronic safety system. It is of course nevertheless possible, although not necessary even in the context of stringent safety requirements, to additionally provide an electronic safety circuit.
It is also possible to configure the engagement element in such way that it lifts out of the thread or tooth set and drops into the next thread flute or tooth space. This embodiment reliably prevents damage to parts even if the motor continues to rotate. Unlike with the use of slip clutches, positioning accuracy is maintained with a displacement unit configured according to the present invention.
A basic idea of the present invention as described above is, of course, applicable to a wide variety of displacement units, such as those required in particular in precision engineering and in optical devices, for example microscopes, automated objectives, etc.
The displacement units can move the carriers rotationally or translationally. In the case of a rotational motion, the transfer element can be, for example, a toothed rack. Instead of a gear, according to the present invention it is also possible to use a xe2x80x9cstarxe2x80x9d whose individual xe2x80x9craysxe2x80x9d are constituted by elastic rods or spring wires, each of which is the engagement element in the tooth set of the toothed rack and, upon contact by the carrier against a stop, is lifted out of the tooth set and then dropped into the next tooth space of the toothed rack.
It is particularly preferred, however, to use the basic idea of the present invention in displacement units in which the carrier is shifted translationally. In this case, the transfer element can be a threaded spindle and the displaced element a carriage. The engagement element preferably comprises at least one spring wire or spring rod whose one end is mounted on the carriage and whose other end resiliently engages into a thread flute of the threaded spindle. Particularly dependable shifting of the carriage is obtained if the engagement element comprises two or more spring wires or spring rods, preferably parallel to one another. The greater the number of spring wires or spring rods, the less play exhibited by the displacement unit. It is also preferred that the orientation of the spring wire or wires or spring rod or rods in the xe2x80x9cundeformedxe2x80x9d state is matched to the pitch of the threaded spindle.
Regardless of whether the carrier performs a translational or a rotational motion, it is further preferred that the drive unit comprises a controllable motor, and in particular an electric motor. Since the principle according to the present invention does not require such precise control of the motor as in the case of conventional displacement units, however, it is also possible to use other motors such as, for example, compressed-air motors.
It is particularly advantageous, however, that the present invention makes it possible, in the context of a displacement between only two positions, to xe2x80x9cdrivexe2x80x9d the carrier, even without electronic safety systems, against stops whose location defines the respective position. Motor control can then be accomplished by way of a xe2x80x9ctime controllerxe2x80x9d that shuts off the motor after a specific time. In conventional displacement units, such a procedure would almost inevitably result in xe2x80x9cjammingxe2x80x9d of parts of the displacement unit orxe2x80x94if the activation time were too shortxe2x80x94possibly in incorrect positioning.
If more than two positions are to be arrived at by the carrier or carriage, or if the carrier or carriage is to be continuously displaced, it is advantageous if at least one position sensor, whose output signal is applied to the drive unit as the xe2x80x9cactualxe2x80x9d signal for the position of the carrier, is provided. This embodiment allows highly precise control of the respective position desired. A position sensor of this kind can be, for example, an incremental displacement sensor.
The displacement unit according to the present invention can of course be used in a wide variety of devices. It is particularly preferred for use in a microscope, however, and in particular in an automated microscope, since it permits the various functions and displacements that are required in an automated microscope to be performed economically and with little installation outlay.